Android -

YES - change the bags - my experience at end of May first week of June in Quetico is that a 40 degree bag is not warm enough.  A 30 degree bag is generally about right, knowing that i can add a fleece jacket or polypro underwear and wool watchcap.  A twenty degree bag will hardly ever be too warm for that time of year.  I normally bring 30 deg bags now.

I have seen ice in the canoes on several trips in the morning, and frost on the tent one morning is not at all unusual.  I think coldest morning was two years ago, on Memorial Day at Dawson Campground - It was no warmer than twenty degrees that morning.